I remember reading some time ago that realtors would put a splash of vanilla extract on a light bulb to make a kitchen smell inviting when showing a house. So I googled it to see what was recommended on the web.
Here's what I found.

There are a variety of scents and ways to produce them.
Simmer pots (spices in a pot of boiling water), Potpourri. Put a few drops of essential oil on your furnace filter each time you change it. Put a few drops of your favorite essential oil on some on cotton balls that you can hide in drawers, on shelves or between the seat cushions on the couch.
Fresh flowers, dryer sheets.

Deodorizing disks will stop bad smells in smaller places like in a shoe closet, in the laundry basket or under your sink.

Problems with some air fresheners:
Many air fresheners (aerosol sprays, electric plug-ins, candles, oil diffusers) release volatile organic compounds (VOCs) such as benzene and toluene into the air.
Terpenes, which are chemicals often derived from citrus oils are not inherently dangerous, but react with ozone to form formaldehyde.
Many aerosols even those advertised as "all natural" contain phthalates, a dispersant which can alter hormone levels and cause other health problems.

Infrequent use to just show a house may not harm you, but it's still better to use a natural alternative.
(see links below)

Pure essential oils that allow you to put a few drops on a cotton ball, may not be a problem, but you have to be careful that they are really pure. Many are diluted to work in dispensers.

What are essential oils:
These naturally occurring, volatile aromatic compounds are found in the seeds, bark, stems, roots, flowers, and other parts of plants.
They tend to change quickly from their solid or liquid state to a gas at room temperature.
They are used for food preparation, beauty treatment, aromatherapy, and health-care practices.

If your home is smelling less than fresh, first find the source of any bad odors. Get a friend to sniff because you may be used to it.
Sprinkle some baking soda on your carpets and sofas. Let it sit for 10-15 minutes, and vacuum it up.

A heavy-duty cleaning approach should eliminate minor unwanted odors and introduce a clean, refreshing scent throughout each room.
Empty the garbage, Run lemon or orange rind along with a few ice cubes thru your garbage disposal.
Try using unscented or subtly scented cleaning products — those that are plant-based or eco-friendly and natural can be good choices.
For heavy pet smells, have your carpets and upholstered items professionally steam-cleaned well in advance.

As a rule of thumb, try not to cook with pungent ingredients for four days prior to a showing.

sticks of cinnamon, and a few cloves in a pot of water; Allspice, fresh ginger, vanilla and orange peels; hidden, open jars of vanilla extract; lavender or uplifting scents such as grapefruit or satsuma; pine

Potpourri, chocolate-chip cookies, gourmet foods, and other baked goods, according to the study

Comments:5 Scents That Make Sense When Selling a Home | Real Estate | US News
"A clean smell and a deodorized smell are two different things. Pulling out scented candles and plug-ins or preparing baked cookies may smell nice to some, but others may think you’re masking a smell or could find the scent appalling. Even worse, the scent could distract the buyer’s ability to make a decision."

"A study at UC-Irvine, found shoppers spent an average of 32 percent more money in a home decor store when it was scented with a simple orange scent, rather than a blend of scents."